1. Field of the Invention
The present invention relates to a method for the non-destructive inspection of a test body using ultrasound, in which ultrasonic waves are coupled into the test body by means of a multiplicity of ultrasonic transducers and the ultrasonic waves reflected inside the test body are received by a multiplicity of ultrasonic transducers and converted into ultrasonic signals, which form the basis of the non-destructive inspection.
2. Description of the Prior Art
The manner of proceeding in non-destructive inspection of a test body by means of ultrasound, and for the purpose of inspecting material for flaws in the material, such as cracks, inclusions or other inhomogeneities in the material comprises coupling ultrasonic waves into the test body, detecting the ultrasonic waves transmitted through or reflected, bent, scattered and/or broken inside the test body as well as evaluating the ultrasonic waves converted into ultrasonic signals.
Using the above as such state-of-the-art methods of inspection, it is possible to detect and evaluate the ultrasonic-wave transmission properties, and reflection properties, of a test body. In this method, which originally stemmed from medical technology (ultrasonic diagnostics), faulty sites, such as cracks in the materials, inclusions or seams in a test body are imaged by means of corresponding evaluation of the received ultrasonic signals as areas with altered reflection properties. Position, shape and size of the faulty sites can be depicted three-dimensionally in a spatially highly resolved manner.
Obviously, the fields of application of this method are evident. Mentioned as examples are application of the method for inspection, examination and detection of the homogeneity properties or solidity properties of the structural parts of buildings (concrete walls, ceiling elements or wall elements, etc.) or crack inspection, for example in railroad wagon wheels or airplane parts.
Employed in many applications of non-destructive material inspection using ultrasound are a multiplicity of ultrasound transducers which are combined for better handling into a so-called ultrasonic probe or emitter array probe. Fundamentally, two types of ultrasonic probes are differentiated. It is called an impulse-echo probe if the probe couples an ultrasonic-wave package into the test body and the ultrasonic waves reflected in the test body are received again by the probe. On the other hand, probes with separate ultrasonic transducers for coupling to and receivers for receiving ultrasonic waves are called transmission/reception probes.
In all the state-of-the-art ultrasonic probes, the single ultrasonic transducers are each connected to a control device which is provided with a separate control electronics, that is an electric control channel, for each ultrasonic transducer with single ultrasonic transducers triggered independently of each other and function, for example, as a ultrasonic transmitter or as a ultrasonic receiver. In particular, such separate triggering allows operating the single ultrasonic transducers with a different phase position and a different amplitude. FIG. 2 shows schematically a state-of-the-art setup of an emitter array system which, using phased array technology, is able to excite ultrasonic waves in the probe at any angle and in any focusing range and to receive the same therefrom. The emitter array system comprises a probe 1 with a multiplicity of single ultrasonic transducers which are all connected to a multi-channel electronic via a cable 2 to transmit electric signals. For each channel, the ultrasonic electronics triggering an ultrasonic transducer is provided with an amplifier 3, an analog/digital converter 4, transmission/reception delay elements 5, a signal adder 6 and a sector image reconstruction unit 7.
In order to carry out a measurement with which the transmission capacity of a probe is to be tested, the control device excites at least one usually, however, a multiplicity of ultrasonic transducers of the emitter array probe may couple ultrasonic waves into the test body for a brief, limited time interval. The resulting ultrasonic wave packages which are inputted are reflected, for example, at faulty sites inside the test body and return as reflected ultrasonic waves to the ultrasonic transducers now operating as receivers and are converted into ultrasonic signals by the receivers and conveyed to the control device for evaluation. The time period between emission and reception of the ultrasonic signals is usually referred to as a measurement cycle. Last but not least, for improved signal detection and evaluation, a multiplicity of such type measurement cycles are carried out successively to obtain an acceptable signal/noise ratio.
In many applications, the goal is to detect inside the test body volume in a finely as possible resolved manner the transmission properties and reflection properties of a test body. For this purpose, the time delay of the transmission cycles is correspondingly adjusted to set the irradiation direction and the focusing depth. The received ultrasonic signals of the single ultrasonic transducers of the emitter array probe are so to say added to the phase delay so that in a transmission cycle an ultrasonic signal is generated for an irradiation angle and, if need be, for a certain focusing depth. This is referred to as a so-called A-image, which is shown in FIG. 3a. The A-image represents the ultrasonic echo along a given “view propagation direction, and a sound propagation direction” through the test body. It can be viewed as a 1-dimensional sectional image like an intersecting line through the test body along which ultrasonic echo signals are shown locally resolved. Sound transmission through the test body at different angles (that is the sonic bundle is pivoted in the test body, preferably within a uniform pivoting plane) permits reconstructing a so-called sector image, which is composed of a multiplicity of single A-images as the graph according to FIG. 3b shows. Additionally, the single echo signals in different colors along the multiplicity of combined A-images yields an interpretable sector image or an interpretable B-image according to the image representation in FIG. 3c, showing sites of increased reflectivity in a cutting plane or a sector inside the test body.
A drawback in using the phased array method for the non-destructive inspection of the material of a test body is however that a great deal of time and measuring effort is required until a test body is inspected as thoroughly as possible as the aim is to obtain sufficiently reliable measuring signals from, if possible, all the regions of the volume for complete signal evaluation. Thus, in one measurement cycle or in a multiplicity of measurement cycles with the same phase triggering of the ultrasonic transducers, only limited information is obtained about the reflection properties in only one volume region or along one given sector of the test body. A very large number of measurements each with different phase triggering is therefore needed to examine the entire test body volume, thus requiring a great amount of time to carry out complete material inspection. Time consuming and work intensive reprogramming is required to set a new irradiation angle, respectively a new focal position.
Another disadvantage is that a given irradiation angle determines the probe aperture, that is, it is not possible to select the aperture optimally for all irradiation angles, which impairs the resolution of the measurements.
A further disadvantage of the phased array method is that for each ultrasonic transducer, a transmission channel and reception channel has to be provided with corresponding electronics connected via electrical connections to the respective ultrasonic transducer. As presently employed ultrasonic probes usually comprise 16 or more ultrasonic transducers, the connections between the probe and the control device usually require a thick, inflexible and therefore difficult to handle cable.
To remedy the abovementioned problems, DE 10 2004 059 856.8-52 describes the principle of a clocked emitter array system in which all the ultrasonic transducers of the emitter array probe are successively excited, whereby in each transmission cycle all the ultrasonic transducers receive the ultrasonic echo signals returning from the test body. The received time signals are stored, and the stored time signals are not evaluated based on a reconstruction algorithm until after termination of the sound transmission through the test body. In this manner, it is possible to reconstruct the ultrasonic signals of one or a multiplicity of irradiation directions, and of focusing depths, from the stored time signals.